In a known arrangement, such a control unit comprises a control element such as a knob or a selector for changing the intensity of the light source. In general, a displacement of the control element can be converted by the control unit into a control signal for controlling the illumination parameter. Such a conversion can e.g. be accomplished by applying a transducer in the control unit. As an example, such a transducer can be a potentiometer or a rotary encoder. By operating the knob or selector, a characteristic of the transducer can be modified and in response to this modified characteristic, the control unit can e.g. generate a control signal to change the intensity of the light source. Often, the functionality of changing the intensity of the light source is combined with a further functionality of turning the light source on or off. This additional functionality can e.g. be realised by a separate switch mounted to the control unit, mounted adjacent to the knob or selector, or the on/off switching can be realised by pushing the knob or selector rather than rotating the knob. Alternatively, the on/off switching of the light source can be realised by a particular position of the selector or knob.
The above described conventional control unit is at present widely distributed and most people are familiar with the operation of such a control unit.
Recently, new light sources for e.g. domestic lighting applications have been developed that provide additional features or controllable parameters compared to a conventional light bulb. Whereas a conventional light bulb only allows the intensity of the light source to be controlled, more recent light sources such as LED fixtures allow the colour of the light source to be controlled as well. As an example, such a LED fixture can comprise a set of LEDs of different colour that can be operated at a different duty cycle or intensity, thereby allowing the colour of the light source as a whole, i.e. as observed by a person, to be modified. As an example on how both a colour and an intensity of a LED fixture can be controlled, reference can be made to WO 2006/107199, incorporated herein by reference. A further example of an illumination parameter that may be controlled is the direction of a light beam of the light source. To that extent, light sources can be equipped with e.g. an electric motor or actuator for displacing or positioning the light source or a part thereof. In order to anticipate on such additional features, control units for controlling such light sources are required. One way of incorporating an additional functionality, such as enabling the colour of a light source to be modified in addition to the intensity being modified, is to provide additional knobs or selectors on the control unit for addressing the different functionalities or illumination parameters. A drawback of such an arrangement is that, in general, the control unit will become larger, require more components and will be more expensive. A further drawback of such an arrangement is that the use of such a control becomes more complex, in particular to an inexperienced user. This can be illustrated as follows: In case the control unit comprises different knobs or selectors for addressing the different functionalities (e.g. a first knob for turning the light source on/off and changing the intensity and a second knob for changing the colour), the user needs to select the appropriate knob for obtaining the required functionality. This may be cumbersome in e.g. domestic applications where, in general, the control of the light source will be directed most of the time to changing the intensity rather than the colour. As an alternative to a control unit with multiple knobs or selectors, one might also consider adding a control layer to the control unit. In such an arrangement, the control unit may e.g. comprise a single knob or selector combined with a switch to change an operating mode of the control unit. Depending on the position of the switch, the displacement of the knob (e.g. a rotation) may result in a change in intensity of the light source or in a change of colour of the light source. A drawback of such an arrangement is that a user who is using the control unit for the first time or for the first time in a long time may find the control unit in a different mode than expected or may be confused when inadvertently operating the switch, thereby obtaining an unexpected operating mode.
In view of the above mentioned recent developments with regard to light sources, it may further be preferred to control such light sources from different locations or using different control units or consoles. In general, it is known to provide an illumination system comprising one or more light sources with multiple control units for controlling the light source (or light sources). As an example, a light source, such as a light bulb, can be controlled (e.g. turned on or off) by different control units (or consoles) from different locations. Such a lighting control system may also comprise more sophisticated control units such as a remote control. Such remote controls can e.g. apply an RF signal to control the light source. As mentioned above, a control unit can be applied to control various parameters of a light source including e.g. the intensity, the colour or an orientation or direction of the light source. Often, a control of these parameters is preferably done from various locations requiring more than one control unit. Known illumination systems having multiple control units are organised using a master-slave concept wherein one control unit operates as the master, the other control units operate as slave. In such a configuration, the flexibility to vary different parameters of the illumination system may be limited, or in order to obtain the required flexibility, complicated control schemes or a substantial configuration effort are required.